Apparatus for the recovery of heat and chemicals from black liquor



April 9, 1940- A. L. HAMM 2,196,496

APPARATUS FOR THE RECOVERY OF HEAT AND CHEMICALS FROM BLACK LIQUOR I Filed March 2; 1938 2 Sheets-$heet 1' MULTIPLE EFFECT EVAPoRAToR 1 IJLJ a WASHER IIIGESTOR l I I co NCENT RATO U DIS$OLVING TANK INVENTOR BY W W ATTORNEYS April 9, 1940. A. L. HAMM 2,196,496

APPARATUS FOR THE RECOVERY OF HEAT AND CHEMICALS FROM BLACK LIQUOR Filed March 2, 195a 2 Sheets-Sheet 2 Patented Apr; 9, {1940 i "STATES OFFICE a 1 2196496' j 9 3 1'1 iv APPARATUS FOR THE RECOVERY OF HEAT ANDiCHEMICALS FROM BLACKLIQUOR Alexander Leopold Hamm, New York, N. Y., assignor to Combustion Engineering Company, 1

' ware 'f v 1110., "New York, N. Y., a corporation of Dela- Application March ,2, 1938; Serial No 193,409

This invention relates to apparatus, for the recovery ofheat and'chemicals from black liquor obtained in the preparation of pulp ffrom wood by. the caustic soda or the sulphate process.

. In general, such apparatus includes evaporators for removing Water fromthe black-liquor,;a ree covery furnace, and a waste heat boiler associated-with the furnace.

v The primary object of my invention is theproe theusual settling hoppers from which accumulations must be removed-periodically.

A further objectof; my. invention resides in incorporating ,scrubbing means offlthe above character within the system for treating the black liquor. l

,How the foregoing, together with such other objects and advantages as will hereinafter appear or are incident to my invention are realized,

is illu strated in preferred form in the accom panying drawings, wherein, Figure 1 .js afmore orless diagrammatic elevational view of arecovery system embodying my invention;

.- Figure 2 is enlarged; sectional elevational 35 view of the recovery. furnace and waste heat boiler of the system; and r u H Figuredillustrates a boiler of modified'form.

Referring to Figural. digested pulp from the digester; 3 .-is passed through the washer 41in 40 which'the residual liquor is washed from thepulp and from which the wash or'black liquor is with:

drawn and passed through a .multiple .efiect evaporator comprisingxa. plurality of evaporating devices-"5. .Ihe liquor isthen passed through a then is ledto -a-scrubber l asby means of apipe 8 for further evaporation.

;.The digester andevaporators are suppliedwith' steam as by means ofpipes 9 leading from suitable stagesof a turbine In which is-connected 'by-means of pipe II "to receive steam from the waste heat .boilerA associated with recovery furnace B. Waste'gases; are led from the boiler to higher.

concentrator 6'tov further increaseits density and .4 Claims. (01.23-26.21

are discharged therefrom through a stack l3 as will further appear'hereinafter.

In passing the black liquor through the multiple effect evaporators the solid-content of the liquor is raised to have ,a fuel density of from 50% to 60% of solids andthis liquor after passing through the concentrator; and scrubber I is raised to have a solid content of 65% of solids or v This concentrated liquor is led from the scrubber I through a pipe [4 to a pump l5, through a heater I6, and through pipe I! to nozzles l8 furnace B under pressure. ,v y Referring to Figure .2, it will be seen thatthe which deliver preheated liquor. into the recovery x v recovery furnace B has its walls lined with bar or exposedupright water tubes which are connected into the circulation of the boiler, the front and rear wall tubes .19, and -receiving water from the lower drum 2| of the boiler by means.

of downcomer tubes '22 connected to a lower header23 and theside wall tubes24 by means of similar downcomer tubes leading-to the lower" headers 25, one of which isprovidedfor each side wall, The rear wall tubes 20 are connected for delivery into thedrum 2| at their upperends,

and. their lower portions are inclinedas 'indi- H cated at 20a. to providewith the refractory lining down pass; for the Waste gasesfrom which the gases-enter the conduit 12, pass through the scrubber! and finally exit through the 'stack I3.

above pointe'dout, the concentrated black. liquor is jpreheated and led to the furnace under pressurebymeans of the fuel nozzles l8, and as it is introduced there is a reduction in pressure which causes some of I the, water in the liquor to flash intoqsteam. vPractically all of the remaining quantities of water are evaporated from the liquortin space and the solid contentor black 2017 a sloping bottom for the furnace. The front ash rang .to the bottom jor hearth; portion of the 'furnacein. almost dry state, where it accumulates in a bed, Preheatedair is admitted into this bed as by means" of inlets 3| vin an amountto keep the bed incandescent l and sufllcient to maintain v a reducing. atmosphere in the bed. The pre-f heated air, is led to "the inlets from a suitable age of moisture contained in the black ash occurs, distillation of the volatiles and burning of the solid combustible materials takeplace, and the sodium sulphate is converted into sodium sulphite which may be withdrawn through a discharge spout 34. i I, Preheated air to complete combustion is introduced into the furnace asby means of a plurality of air inlets 35, the air being ledto the inlets by means of conduits 36 and 31.

The hot burning gases rise from the bed in countercurrent to the falling black ash and as the gas stream travels upwardly heat is absorbed by the wall tubes for the generation of steam.

The furnace is initially heated up by introducing fuel as by means of a suitable burner 38, after which it is self-sustaining.

- Since the furnace is tall the gases have a large distance to travel through so that condensation of chemicals carried in the gas stream occurs and the particles gravitate to the hearth for recovery together with other combustible particles of dry solids which may have been carried upward in the gas stream. 7

Any fine substances that are carried on through the'boiler are finally delivered into the scrubber l. 'I'hescrubber is provided with revolving discs 1a which dip into the'liquor and expose a film of liquor to the waste gases, thereby not" only evaporating water from the-liquor but also washing the gases by-the adhesion ofthe entrained solids onto the wet discs. 7 These washed out solids add to the concentration of liquor and are ,returned to the recovery furnace with 'the concentrated liquor.' a

It will thus be seen that by locating the scrubber l at the bottom of the downward boiler pass 30 the carry-over of the-boiler is delivered thereto and treated therein so that settling hoppers such as have been heretofore employedare unnecessary. Thus, the labor of removing and disposing of the accumulations in the hoppers is eliminated and the usual dust handling, problem-"is overcome, it being noted that substantially all of the chemical and combustible solids are recovered from the waste gases before the. gases discharge to the atmosphere. i In Figure 3 I have' illustrated a modified waste heat boiler having alower drum 39;an upper drum M3, connecting banks vof-1boiler tubes 4i,

andbaffles 52 extending from the lower drum to the upper drum. Aboiler' casing 43 is provided,

the top wall M of which" is spaced Iabovethe upper drum to provide a top gas's'pace 45. The upright walls 46 of the casing and the bafiles 42 provide two passesffor the boiler. The products of combustion leaving the recovery furnace B i the upper drum 4D through the top gas space45, and then downwardly through the rear pass 48.

i The gases are led from the rear pass to the scrubadmitting the required air for combustion into said furnace; a waste heat'boiler associated with source as by means of a conduit 32 and air chame of vertically disposed tubes overhanging the furnace and paralleling the upward flow of, the gas stream from the furnace, a final downward pass for the waste gases, and an .outlet for the discharge of waste gases at the bottom of said pass; a scrubber connected to said outlet to recover carry-over from the discharging waste gases; means for introducing"black liquor into said scrubber; means fordischarging-waste gases freed of such carry-overfrom said scrubber; and means for leading treated black liquor and recovered carry-over to said nozzle means.

2. In apparatus for recovering chemicals from blackliquor, the] combination of a water .wall lined recovery furnace; nozzle means for introducing black liquorinto said furnace; means for admittin the required air for combustion into said furnace; a waste heat boiler located above the furnace, said boilerhaving an upward pass in direct communicationwith the furnace, a rear downward pass, vertical boiler tubes in said upwardpass paralleling the upward flow of the gas stream from the furnace and constituting a slagging sectionof the boiler, vertical boiler tubes in said rear pass and baffle means associatedwith the boiler tubes to provide said passes; an outlet at the bottomof said rear pass; a scrubber having an inlet connected tosaid outlet whereby waste gases and carry-over discharge from the boiler into said scrubber; means forintroducing black liquor into said scrubber; means for discharging waste gases freed of such. carry-over from said scrubber; and means for leading treated black liquor and recovered carry-over to said nozzle means.

3. In apparatus for recovering chemicals from black liquor, the combination of a water Wall lined recovery furnace; nozzle means for intro- ;luring black liquor into said furnace; means for admitting the required air for combustion. into said furnace;- an'upright-waste heat boiler above said furnace, said boiler having an upper drum, a lower drum, a front set ofvertical boiler tubes connecting said drums and constituting a slagging section of the boiler, a rear set of vertical boiler tubes connecting said'drum andbaffie means extending from thelower'to the upper drum between said sets of boiler tubes; casing structure associated with .saidb'oiler to provide'withsaid baffle means a boiler pass in which the front is'located through which said gases passin downward flow, and an upper chamberabove said upper drum establishing communication from "the upward passto the downward pass; a scrubber evaporator at the-bottom of said rear pass in communication therewith to receive waste gases and carry-over from saidjrear pass; meansfor introducing black liquor" into. said scrubber evaporator; means for discharging waste gases freed of such carry-over from said scrubber evaporator, and means for leadingltreated liquor and recovered carry-over to said nozzle means.

4. In apparatus for recoveringchemicals from black liquor, the combination of 1a water wall lined recovery furnace; nozzle means) for introducing black liquor into'sa'id furnace; means for admitting the required air .for combustion into said furnace; an upright waste heat boiler above said furnace, said boiler havingan upper drum, the furnace, said boiler having a slagging section a lower drum, a front set "of vertical boiler tubes connecting said drums and extending directlv over the furnace to provide with the water walls of the furnace a tall cooledpassage through which the gases flow upwardly in parallel relation to the vertical boiler tubes, a rear set of vertical boiler tubes connecting said drums, bafliing be-, tween said sets of tubes for providing a rear downward pass in which the rear set of vertical "and carry-over from said rear pass; means-for introducing black liquor into said scrubber evaporator, and means for leading treated liquor and recovered carry-over to said nozzle means."

ALEX. L. 

